CHAPTER 8 GEARED SYSTEMS AND VARIABLE-SPEED MECHANISMS GEARS AND GEARING Gear tooth terminology Gears are versatile mechanical components capable of performing many different kinds of power transmission or motion control. Examples of these are • • • • Changing rotational speed. Changing rotational direction. Changing the angular orientation of rotational motion. Multiplication or division of torque or magnitude of rotation. • Converting rotational to linear motion and its reverse. • Offsetting or changing the location of rotating motion. Gear Tooth Geometry: This is determined primarily by pitch, depth, and pressure angle. dedendum: The radial distance between the pitch circle and the dedendum circle. depth: A. | _CHAPTER 8 GEARED SYSTEMS AND VARIABLE-SPEED MECHANISMS GEARS AND GEARING Gear tooth terminology Gears are versatile mechanical components capable of performing many different kinds of power transmission or motion control. Examples of these are Changing rotational speed. Changing rotational direction. Changing the angular orientation of rotational motion. Multiplication or division of torque or magnitude of rotation. Converting rotational to linear motion and its reverse. Offsetting or changing the location of rotating motion. Gear Tooth Geometry This is determined primarily by pitch depth and pressure angle. Gear Terminology addendum The radial distance between the top land and the pitch circle. addendum circle The circle defining the outer diameter of the gear. circular pitch The distance along the pitch circle from a point on one tooth to a corresponding point on an adjacent tooth. It is also the sum of the tooth thickness and the space width measured in inches or millimeters. clearance The radial distance between the bottom land and the clearance circle. contact ratio The ratio of the number of teeth in contact to the number of those not in contact. dedendum circle The theoretical circle through the bottom lands of a gear. dedendum The radial distance between the pitch circle and the dedendum circle. depth A number standardized in terms of pitch. Full-depth teeth have a working depth of 2 P. If the teeth have equal addenda as in standard interchangeable gears the addendum is 1 P. Fulldepth gear teeth have a larger contact ratio than stub teeth and their working depth is about 20 more than that of stub gear teeth. Gears with a small number of teeth might require undercutting to prevent one interfering with another during engagement. diametral pitch P The ratio of the number of teeth to the pitch diameter. A measure of the coarseness of a gear it is the index of tooth size when . units are used expressed as teeth per inch. pitch A standard pitch
